MEIOTIC BEHAVIOR OF THE X1X2Y1Y2 QUADRIVALENT OF THE PRIMATE ALOUATTA-CARAYA

A multiple sex chromosome system was found in three unrelated individu als of the primate Alouatta caraya. This mechanism is originated by a translocation between the Y chromosome and one of the autosomes (A7). Mitotic karyotypes show two small, acrocentric chromosomes (A(Y) and Y -A), which are the translocation products. In metaphase I of male meio sis, there is a very long chain quadrivalent in which the order of the element is: X-Y-A-A7-A(Y). Segregation in the quadrivalent is alterna te and gives balanced products. Synaptonemal complex karyotypes at pac hytene show the structure of the quadrivalent made by the four axes. T here is a slight difference in the relative length of AY and YA and th e kinetochore of A7 aligns with that of AY The synaptic pattern and ch anges in the quadrivalent during pachytene are described. Thin section s of the quadrivalent body show that the chromatin packing in the sex chromosome region is different from that of the autosomal region. This X1X2Y1Y2/X1X1XX2 sex chromosome system may be extended among other me mbers of the genus Alouatta.